1. Technical Field
The present invention relates to a heat dissipating sheet and a plasma display device including the same and, more particularly, to a heat dissipating sheet that has an improved structure such that a temperature distribution of a heating element is uniform and which can be easily attached/separated to/from a plasma display device, and a plasma display device including the heat dissipating sheet.
2. Description of the Related Art
A plasma display device is a flat display device that displays an image using a gas discharging phenomenon. The plasma display device has good displaying characteristics, such as display capacity, brightness, contrast, after-image, and viewing angle. Also, the plasma display device can display on a large screen with a thin main body, and it is thus considered to be a display device of the next generation and a replacement for the cathode ray tube (CRT) device.
The plasma display device includes a plasma display panel (PDP) which includes a front panel and a back panel, a chassis base, a back surface which includes a circuit unit for driving the PDP, and a heat dissipating sheet disposed between the PDP and the chassis base.
Since the plasma display device uses a discharging operation for displaying images, the panel which displays images generates a lot of heat.
Conventionally, the heat dissipating sheet is manufactured using a resin composition mixed with thermal conductive filler, such as copper powder, graphite powder or aluminum powder.
However, the heat dissipating sheet with the above structure has a low thermal conductive coefficient of about 1 W/mK, and thus it has a weak heat dissipating function. Especially, when heat dissipation in the panel plane direction is not sufficient, the uneven temperature distribution due to the discharging intensity cannot be eliminated promptly. Thus, brightness is lowered at the discharging cell, in which more heat accumulates, and this results in an after-image, which is the brightness difference between a discharging cell and a non-discharging cell. As a result, the brightness of the entire PDP is lowered. Moreover, when the discharging strength is raised to improve the brightness of the plasma display device, the panel generates more heat.
In addition, if the temperature is distributed unevenly on a panel that is manufactured using glass material, durability of the panel is lowered and the panel may crack due to temperature stress.
In order to improve the uneven temperature distribution and thermal conductive function, a high thermal conductive heat dissipating sheet made of high oriented graphite is used. However, such a high thermal conductive heat dissipating sheet has poor adherence with a panel which is manufactured using glass material, and thus the heat dissipating function is lowered.
In addition, the high thermal conductive heat dissipating sheet has weak coherence between particles due to the characteristic of the material, and this can cause a brittle fracture problem due to weak flexibility thereof.
Moreover, if the heat dissipating sheet is removed in order to repair the PDP, some of the heat dissipating sheet may remain on the panel, thus requiring additional manual work.
Japanese Laid-open Patent No. hei 6-216285 discloses another example for improving the heat dissipating function. It discloses a heat dissipating sheet manufactured using a thermal conductive woven fabric. The thermal woven fabric is woven using carbon fibers, and the fabric is disposed between a heat generating body, such as an electric or electronic element, and a heat sink to dissipate the heat generated by the heat generating body.
However, the heat generating body and the heat sink may include a non-planar portion, and may include a distorted portion due to the heat generated by the heat generating body. If the flatness of the heat generating body and of the heat sink is lowered due to the non-planar portion or the distorted portion, the heat dissipating sheet cannot be closely adhered between the heat generating body and the heat sink. In addition, according to the conventional art, a unit for preventing inferior coherence is not provided, thus lowering the heat dissipating function.
Moreover, the heat dissipating sheet woven by the carbon fiber includes a bent portion where the carbon fibers cross each other, and thus the flatness is lowered due to the bent portion. Also, since the carbon fiber is strained and the stress is concentrated in the bent portion, the flexibility of the fabric is lowered and the coherence of the heat dissipating sheet is degraded.